1. Field of the Invention
The present invention relates to an image reading apparatus for reading the image of an original on a light transmitting member through scanning with a reading means, such as a reading unit.
2. Related Background Art
Generally speaking, when reading the image of an original by a conventional image reading apparatus, the following two methods are available.
One of the methods is a stationary original reading method in which the original is set in position on an original glass stand, which serves as the light transmitting member, in a predetermined manner, and in which the original remaining stationary on the original glass stand is scanned by an optical carriage serving as a movable image reading means, whereby the image of the original is read.
The other method is a flowing original reading method in which the original is conveyed at a predetermined speed to be read at a predetermined reading portion where a stationary optical carriage is arranged.
As compared with the former method, i.e., the stationary original reading method, the latter method, i.e., the flowing original reading method, is more advantageous, for example, in that the optical carriage can remain stationary, and there is no need to reciprocate the optical carriage each time reading is to be performed.
Further, as a result of the recent digitization of image reading units for use in copying machines or the like, a single reading suffices where a plurality of copies of an image are to be made, which makes the flowing original reading method most advantageous.
That is, in digital image reading and recording, when a plurality of copies of an image are to be made, the image is read by a single flow reading and can be stored in a digitized form in an amount corresponding to the number of copies required.
Now that it has become possible to store read images in memory, an image reading apparatus is required to be capable of reading images as quickly as possible.
In the conventional technique described above, it is necessary to read a standard white plate for shading compensation at the time of image reading to determine the standard white for the image read.
When this standard white plate has been soiled as a result of the conveyance of originals for reading, it is difficult to correctly perform the cleaning of the standard white plate, so that it is necessary to perform a periodical maintenance or the like on the standard white plate.